This doesn't match the physics. The formula for drag is:

rolling_drag + ( (coef_of_drag * area) * (velocity**2) )

• rolling_drag - a function of tires, wheel bearings and transmission losses
• coef_of_drag - the coefficient of drag is determined by vehicle shape, air density and Reynolds number
• area - the cross section of the vehicle
• velocity - speed

The power needed to move the vehicle is the speed multiplied by the drag. Plotting this gives the power required as a function of speed. Then using a simplifying assumption of a fixed ratio of gasoline to power conversion, one can plot the expected MPG vs MPH speed:

There is pretty good agreement between various benchmarks and the predicted performance for a warmed-up vehicle. The key is getting the vehicle warmed up, both the ICE and transaxle. But there are other effects that keep us from achieving the maximum: (1) warm-up, (2) braking losses (even with regeneration), (3) critical transaxle transition speeds (42 mph in the Prius) and (4) non-linear ICE efficiency (it gets lossy at higher rpms.)

The Japanese, single tank record also was in the 20-25 mph range thanks to the modest speeds of the commuting route. Even the first Prius marathon used speeds below 40 mph. During the Insight marathon, the average speed was 18 mph and for the last three days, 15 mph. The physics tell us why.

Bob Wilson

 

If only that were really the case... The physics explanation is posted above, but anyone whose ever driven a bicycle knows it's easier to keep a low speed than a high one. The increased momentum is a result of the speed-- the speed is the result of the energy expended by the engine, or in our bicycle example, the cyclist himself.